1. Field of the Invention
The present invention pertains to photoimaging and to the use of positive-working photoresists, particularly for imaging in the production of semiconductor devices.
2. Description of Related Art
Polymer products are used as components of imaging and photosensitive systems and particularly in photoimaging systems such as those described in Introduction to Microlithography, Second Edition by L. F. Thompson, C. G. Willson, and M. J. Bowden, American Chemical Society, Washington, D.C., 1994. In such systems, ultraviolet (UV) light or other electromagnetic radiation impinges on a material containing a photoactive component to induce a physical or chemical change in that material. An image or latent image is thereby produced which can be used for semiconductor device fabrication.
Although the polymer product itself may be photoactive, generally a photosensitive composition contains one or more photoactive components in addition to the polymer product. Upon exposure to electromagnetic radiation (e.g., UV light), the photoactive component acts to change the Theological state, the solubility, the surface characteristics, refractive index, the color, the electromagnetic characteristics or other such physical or chemical characteristics of the photosensitive composition as described in the Thompson et al. publication supra.
For imaging very fine features at the submicron (sub-μm) level in semiconductor devices, electromagnetic radiation in the deep or vacuum ultraviolet (UV) is typically employed. Positive working resists generally are utilized for semiconductor manufacture. Lithography in the violet or the UV at 365 nm (I-line) using novolak polymers and diazonaphthoquinones as dissolution inhibitors is a currently established chip technology having a resolution limit of about 0.35-0.30 μm. Lithography in the deep UV (DUV) at 248 nm using p-hydroxystyrene polymers is known and has a resolution limit of 0.35-0.18 μm. There is strong impetus for future photolithography at even shorter wavelengths, due to decreasing lower resolution limit with decreasing wavelength (i.e., a resolution limit of 0.18-0.13 μm for 193 nm imaging). Photolithography using 193 nm exposure wavelength (obtained from an argon fluorine (Ar—F) excimer laser) is a leading candidate for future microelectronic fabrication using 0.18 and 0.13 μm design rules. Photolighography using 157 nm exposure wavelength (obtained using an F2 laser source) may be used for future microelectronics fabrication using 0.100 μm or less design rules. The opacity of traditional UV and deep-UV organic photoresists at 193 nm precludes their use in single-layer schemes at this wavelength. Recently new photoresist compositions comprising cycloolefin-maleic anhydride alternating copolymers have been shown to be useful for imaging of semiconductors at 193 nm (see F. M. Houlihan et al., Macromolecules, 30, pages 6517-6534 (1997); T. Wallow et al., SPIE, Vol. 2724, pages 355-364; and F. M. Houlihan et al., Journal of Photopolymer Science and Technology, 10, No. 3, pages 511-520 (1997)).
Comb polymers are a particular class of branched polymers wherein one or more branch (polymer) segments are linked along a linear (polymer) backbone segment. Comb polymers may also be described as linear polymers with polymeric arms. Such polymers typically are prepared by copolymerizing a conventional monomer with a macromer. Macromers are defined by Kawakami in the “Encyclopedia Of Polymer Science And Engineering”, Vol. 9, pp. 195-204 (John Wiley & Sons, New York, 1987) to be polymers of molecular weight ranging from several hundred to tens of thousands, with a functional group at the end that can further polymerize, such as an ethylenic, an epoxy, a dicarboxylic acid, a diol or a diamino group. U.S. Pat. No. 5,061,602 discloses the use of such a polymer as a binding agent in a negative-working photopolymerizable material suitable for producing printing forms or resist patterns. The polymer binder disclosed consists of a film-forming copolymer that has a multi-phase morphology where at least one phase has a glass transition temperature below room temperature and at least one other phase has a glass transition temperature above room temperature. The copolymer has an average molecular weight (weight average) of more than 10,000, and is produced using an ethylenically unsaturated macromer with an average molecular weight (weight average) of 1000 to 100,000. The use of graft (comb) copolymers having acid functionality in certain negative-working photosensitive compositions, such as solder masks, has published (see PCT International Publication No. WO92/15628.
There is a critical need though for other novel resist compositions for use at 193 nm or lower, and particularly at 157 nm, that have not only high transparency at these short wavelengths but also other suitable key properties, including good plasma etch resistance and adhesive properties. This invention addresses this critical need by providing new advantageous compositions and associated processes, comprising graft (comb) copolymers, which have these key properties.